1. Field of the Invention
The present invention relates to an optical system and a projection display device. Particularly, the present invention relates to an optical system and a projection display device both of which can provide high-contrast images and multi-primary color/3-dimensional images for a projection type projector.
2. Description of Related Art
Conventionally, a 3-panel type projector using three pieces (red, green, blue) of modulation devices is general in the projection display device (projector). Depending on the kind of devices, the 3-panel type projectors comprise LCD (Liquid Crystal Display) projector, DLP (Digital Light Processing) projector, LCOS (Liquid Crystal on Silicon) projector and so on. However, there is a possibility that precise color reproduction couldn't be attained by only a single 3-panel type projector since its reproducible area is limited to an area represented as the sum of 3-dimensional color vectors in a 3-dimensional color space.
Therefore, there are proposed multi-primary color projectors each using four or more colors in order to attain more accurate color reproduction (e.g. Japanese Patent Laid-Open Publication Nos. 2000-253263 and 2000-338950). In common with these projection display devices, there are adopted two projectors: one for inputting two data about primary colors C1 and C2 where emission spectrums are distributed in the wavelength bands of different visible ranges and the other for inputting two data about primary colors C3 and C4 where emission spectrums are distributed in the wavelength bands of different visible ranges, which are also different from the wavelength bands of C1, C2. Then, these projectors project respective lights corresponding to the primary colors' data on a screen, realizing a color reproduction range of 4-primary colors broader than the color reproduction range of 3-primary colors.
Meanwhile, there is also known a multi-primary color (6-primary color) projection display device having a boarder color reproduction range than that of the above projector adopting 4-primary colors (e.g. Masahiro Yamaguchi et al., “High-fidelity video and still-image communication based on spectral information: Natural Vision System and its applications”, http://www.isl.titech.ac.jp/{tilde over ( )}guchi/NV/EI06-6062-16c.pdf, Searching Date: Oct. 5, 2007). FIG. 1 is a structural view showing an example of this multi-primary color (6-primary color) projection display device. The shown multi-primary color projection display device comprises a 6-primary color signal processing and converting block 1 and two DLP projectors 8A, 8B thereby to project an image on a screen 9.
The 6-primary color signal processing and converting block 1 has two signal transmission routes for the DLP projectors 8A, 8B. In accordance with one route, dual-linked SDI signals from a decoder 2 are once stored in an output memory unit 3 and directly supplied to the DLP projectors 8A, 8B as they are in the form of TMDS (Transition Minimized Differential Signaling). In accordance with another route, the dual-linked SDI signals stored in the output memory unit 3 are once formatted by a format converter 4 and successively converted to 6-primary colors by a 3-6 color conversion unit 5. Then, the so-converted SDI signals are supplied to the DLP projectors 8A, 8B. Note, the output memory unit 3 and the 3-6 color conversion unit 5 are together controlled in operation by a multi-primary color conversion workstation unit 6 and a 3-primary color conversion workstation unit 7, allowing the SDI signals to be converted to 3-primary colors up to 6-primary colors.
Besides the DLP projectors 8A, 8B, the above-mentioned projection display may adopt another projector, for example, a LCOS projector shown in FIG. 2. In FIG. 2, white light is emitted from a specified lamp (e.g. xenon lamp, ultra-high pressure mercury lamp, laser diode, light emission diode, etc.) in a lamp house 11. Then, the white light is changed to a parallel light by a condenser lens 12 and successively reflected by a cold mirror 13 for eliminating UV light or IR light unnecessary for a display device or interposed optical components. Then, the so-reflected light is transmitted through an integrator (rod integrator, flyeye integrator, etc.) 14 and a sequent field lens 15 thereby to enter a B/RG dichroic mirror 16.
The B/RG dichroic mirror 16 resolves incident illumination light to a light containing the wave bands of both red light and green light and a blue light, so that the former light (red and green) enters a RG mirror 17, while the latter light (blue) enters a B mirror 18. In the former light reflected by the RG mirror 17, its red light component is transmitted through a R/G dichroic mirror 19 thereby to enter an R field lens 24, while the green light component is reflected by the R/G dichroic mirror 19 thereby to enter a G field lens 20.
Regarding the green light component transmitted through the G field lens 20 and the red light component transmitted through R field lens 24, their S-polarization components are reflected by wire grids 21, 25 as polarization split elements thereby to enter a G device 23 and an R device 27 through a G quarter-wave (λ/4) plate 22 and an R quarter-wave (λ/4) plate 26, respectively. After light modulation at the G device 23 and the R device 27 with green signal and red signal of an image to be displayed from the 6-primary color signal processing and converting block 1, their P-polarized lights on light modulation are transmitted through the G, R quarter-wave (λ/4) plates 22, 26 and the wire grids 21, 25 thereby to enter an RGB composite dichroic prism 32.
On the other hand, regarding the blue light component reflected by the B mirror 18, it is transmitted through a B field lens 28 and the light's S-polarization component is reflected by a wire grid 29 thereby to enter a B device 31 through a B quarter-wave (λ/4) plate 30. After light modulation at the B device 31 with blue signal of the image to be displayed from the 6-primary color signal processing and converting block 1, the S-polarized light on light modulation is transmitted through the B quarter-wave (λ/4) plate 30 and the wire grid 29 thereby to enter the RGB composite dichroic prism 32.
The RGB composite dichroic prism 32 recombines respective P-polarization components of incident green, red and blue lights on light modulation. The so-combined light is transmitted through a PJ lens 33 to form an image on a screen.
Depending on the characteristics of the RG mirror 17, the B mirror 18 and the R/G dichroic mirror 19, respective red, green and blue lights incident on the R device 27, the G device 23 and the B device 31 in the LCOS projector 8A have wavelength bands shown with R2, G2 and B2 in (A) of FIG. 3, respectively. On the other hand, in the LCOS projector 8B, respective red, green and blue lights incident on the R device 27, the G device 23 and the B device 31 have wavelength bands shown with R1, G1 and B1 in (B) of FIG. 3, respectively. Therefore, the information about a color image formed on the screen 9 as a result of projecting lights through these projectors 8A and 8B is represented in a chromaticity diagram in (C) of FIG. 3, by its 6-primary color reproduction range obtained by linking six wavelength bands with each other. Obviously, this 6-primary color reproduction range is wider than the above 4-primary color reproduction range. Thus, it becomes possible to reproduce even hematic color, purple and cobalt blue, all of which could not be reproduced by the conventional RGB color reproduction display system. For this reason, the above-mentioned multi-primary color projection display device has begun to be used in an image evaluation where the quality of color reproduction plays a significant role, for instance, reproduction of art objects such as pictures and ceramic wares, reproduction of medical science images and so on.
In another prior art, there is also known a multi-color or three-dimensional display device which utilizes a RGB color band separation filter in addition to two projectors in piles (e.g. combination of one projector for audience's left eye and another projector for right eye) (see http://www2.aimet.ne.jp/nakahara/3dart/3generi9.html, Search Date: Oct. 9, 2007).